This invention relates to the dimerization of olefins in a reactor system. In one respect this invention relates to an improved method for the preconditioning, startup and operation of a reactor for the dimerization of olefins.
The dimerization of olefins is a well-known process in the art; see, e.g., Hutson and Carter, U.S. Pat. No. 3,631,121 (1971) and Zuech, U.S. Pat. No. 3,485,881 (1969). Olefin dimerization processes are applicable to olefins in general, however, dimerization is an especially attractive method for producing butylenes from ethylene for subsequent use in alkylation, dehydrogenation to butadiene and other chemical processes.
Zuech discloses in U.S. Pat. No. 3,485,881 that in dimerization reactions catalyzed by a first catalyst component containing nickel and a second catalyst component containing aluminum, the catalyst components are generally combined in proportions in the range from about 0.5 to about 20 moles of aluminum in the second component per mole of nickel in the first component. It was found desirable to use the upper portion of this range when desirable to scavenge catalyst poisons from the system. However, in order to minimize fouling of the interior reactor surface with polymer, it is now generally preferred that the aluminum/nickel molar feed ratio be relatively low, e.g., in the range of about 2.1:1 to about 7:1, as disclosed in my U.S. Pat. No. 4,242,531. Further, with the use of such relatively low catalyst aluminum/nickel ratios, the deposits that do form in the reactor and heat exchangers can be readily removed by washing with a 10 weight percent acetic acid solution.
Problems arise in dimerization processes in that the process suffers from low selectivity to the dimer, with much of the feed being converted to trimers and product heavies. It is known that selectivity can be improved by using shorter reactor residence time, but the disadvantages of this approach are low ethylene conversion and low catalyst productivity. Other problems arise when the feed stream is low in olefin concentration, e.g., only a small amount of ethylene with the remainder of the feed stream being gases such as hydrogen, methane, ethane, etc.
Accordingly, it is an object of this invention to provide an improved and more economical process for olefin dimerization.
Another object of this invention is to provide an olefin dimerization process with improved olefinic dimer selectivity and yield.
Another object of this invention is to provide an improved method for pre-conditioning and starting up a reactor for the dimerization of olefins, such that improved olefinic dimer selectivity and yield are obtained.
Other aspects, objects and advantages will be apparent from a study of this disclosure, the drawings and the appended claims.